The present invention relates to an esterase gene and its use.
Cyclopentenolones of formula I: 
wherein R1 is C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl or C1-C4 haloalkyl, are useful as the important alcohol components in a group of ester compounds, commonly called xe2x80x9csynthetic pyrethroids,xe2x80x9d having excellent insecticidal activity.
For example, the compound of formula II below, an ester of 4-hydroxy-3-methyl-2-(2-propynyl)cyclopent-2-en-1-one with 2,2,3,3-tetramethylcyclopropanecarboxylic acid, is an excellent insecticide having very strong knockdown activity and mortal activity (see, e.g., JP-B 50-15843/1975). 
The cyclopentenolones of formula I include two kinds of optical isomers because they have an asymmetric carbon atom at position 4. In the case of synthetic pyrethroids containing such optical isomers as the alcohol components, it is well known that the difference in optical isomerism between these alcohol components makes a great difference in their insecticidal effects. For example, the compound of formula II above has been found to exhibit several times as excellent insecticidal activity in the case of an ester of (S)-4-hydroxy-3-methyl-2-(2-propynyl)cyclopent-2-en-1-one as in the case of an ester of the corresponding (R)-4-hydroxy-3-methyl-2-(2-propynyl)cyclopent-2-en-1-one.
For these reasons, there has been a great demand for the development of a method for separating and obtaining the optical isomers of cyclopentenolones of formula I as the intermediates of drugs, agricultural chemicals or other active products in an industrially favorable manner. In addition, for this purpose, in order to prepare a microorganism, for example, by a gene engineering technique, which microorganism can produce an excellent esterase capable of acting upon an organic carboxylic acid ester of a cyclopentenolone of formula I for asymmetric hydrolysis of the ester, the search of a gene coding for such an esterase has also been eagerly desired.
Under these circumstances, the present inventors have extensively studied and found an esterase gene coding for an esterase capable of acting upon an organic carboxylic acid ester of a cyclopentenolone of formula I for asymmetric hydrolysis of the ester to produce the cyclopentenolone in (S)-form with high optical purity, thereby completing the present invention.
Thus, the present invention provides:
1) An isolated esterase gene coding for an esterase capable of causing asymmetric hydrolysis of an organic carboxylic acid ester of a cyclopentenolone of formula I: 
wherein R1 is C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl or C1-C4 haloalkyl, to produce the cyclopentenolone of formula I in (S)-form, and hybridizing to the base sequence of SEQ ID NO:1 (hereinafter referred to as the present gene);
2) The isolated esterase gene according to item 1, wherein the homology of the gene to the base sequence of SEQ ID NO:1 is 90% or higher.
3) The isolated esterase gene according to item 1, having a base sequence coding for the amino acid sequence of SEQ ID NO:2.
4) The isolated esterase gene according to item 1, having the base sequence of SEQ ID NO:1.
5) A plasmid containing the isolated esterase gene of item 1, 2, 3 or 4 (hereinafter referred to as the present plasmid).
6) A transformant obtained by transformation with the plasmid of item 5 (hereinafter referred to as the present transformant).
7) The transformant according to item 6, which is a microorganism.
8) An esterase produced by a microorganism having the isolated esterase gene of item 1, 2, 3 or 4 (hereinafter referred to as the present esterase).
9) The esterase according to item 8, wherein the microorganism having the isolated esterase gene of item 1, 2, 3 or 4 is the transformant of item 6.
10) A process for producing en esterase, which comprises cultivating the transformant of item 6 to produce an esterase capable of causing asymmetric hydrolysis of an organic carboxylic acid ester of a cyclopentenolone of formula I: 
wherein R1 is C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl or C1-C4 haloalkyl, to produce the cyclopentenolone of formula I in (S)-form (hereinafter referred to as the present production process).
11) A method for the optical resolution of a cyclopentenolone of formula I: 
wherein R1 is C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl or C1-C4 haloalkyl, which comprises allowing the esterase of item 8 to act upon an organic carboxylic acid ester of the cyclopentenolone of formula I for asymmetric hydrolysis of the ester; and separating the cyclopentenolone of formula I in (S)-form from the ester of the corresponding enantiomer thereof.
12) The optical resolution method according to item 11, wherein the cyclopentenolone of formula I is 4-hydroxy-3-methyl-2-(2-propenyl)cyclopent-2-en-1 -one.
13) The optical resolution method according to item 11, wherein the cyclopentenolone of formula I is 4-hydroxy-3-methyl-2-(2-propynyl)cyclopent-2-en-1-one.